[Ushiba, Aso]

The attached figures show the cavity scan of OMC with X-arm single arm lock.

From this, FSR = 10.2sec

Zoom into a peak, the FWHM is 0.017sec

Finesse = FSR/FWHM = 590.

We can also calibrate the PZT actuation efficiency.

PZT output changed 4093cnts over 1 FSR.

Since the half length of OMC, Lomc = 0.716m, the FSR of OMC is c/(2*Lomc) = 209MHz.

Therefore, the PZT actuation efficiency in frequency is,  Af = 209e6/4093 = 5.1e4 Hz/cnt.

Using df/fc = dL/L, the actuation efficiency in length is, AL = Af*L/fc = 1.3e-10 m/cnt